Tape with solder forms for semiconductor devices

ABSTRACT

An electronic component with insulative tape-held solder forms is disclosed. Electronic components may be any of the integrated circuit chips, chip packages and printed circuit boards. The solder forms are coupled to conductive pads of the electronic component through through-holes in the insulative tape. The solder forms may be shaped as balls, cylinders, polygonal boxes, barrels, or hour-glasses. The insulative tape is thermally conductive and heat resistant. The tape may be made of an organic material such as an elastomer. The tape may further have impregnated materials such as ceramic, aluminum nitride, or solder flux to improve its thermal, mechanical, and/or electrical properties.

This is a Continuation Application of application Ser. No. 08/648,308,filed May 13, 1996, abandoned; which is a continuation of applicationSer. No. 08/412,132, filed Mar. 28, 1995, abandoned; which is adivisional of application Ser. No. 08/299,520, filed Sep. 1, 1994, nowU.S. Pat. No 5,497,938.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of semiconductor chippackaging technologies and, more particularly, to transferring solderforms to chips, chip packages or printed circuit boards.

2. Description of the Related Art

A ball grid array (BGA) chip package 10 shown in FIG. 1A solves thepin-out problem of a conventional surface mount chip package by havingan array of output pads 9 on one side of the package instead of havingonly metal leads at the outer perimeter of the chip package. BGA Chippackage 10 may have fully populated solder forms, as shown in FIG. 1B,or partially populated solder forms, as shown in FIG. 1C. Solder forms11 are attached to chip package 10 at the end of the chip manufacturingprocess, and the solder form attachment occurs before chip package 10 isattached to a printed circuit board (PCB). Solder forms 11 are used tomake electrical connections between chip package 10 and the PCB.

One conventional scheme for attaching solder forms 11 to chip package 10is to position and transfer the solder forms to chip package 10 one at atime mechanically in an assembly line. Another prior art scheme is to(a) place, in the assembly line, a matrix of solder forms 21 on afixture 23 that holds solder forms 21 temporarily and (b) transfer allof solder forms 21 to chip package 20 at once in the assembly line, asshown in FIG. 2. The advantage of the second scheme over the first isits speed. However, both schemes require sophisticated and expensiveassembly equipment having stringent process controls that may cost ashigh as one to one and a half million dollars. Thus, it is costly andimpractical to have a large number of these machines in the assemblyline.

To overcome the drawbacks of the prior art, the present inventionprovides cost-effective and time-saving methods for transferring solderforms to IC chips, chip packages or PCBs by requiring a small number ofsophisticated equipment off-line and a simplistic, reduced accuracyequipment base in the assembly line.

The present invention provides a two-step process to transfer the solderforms: (a) the solder forms are accurately positioned and placed on aroll of tape off-line using high speed, precision equipment, and (b) thesolder forms on the roll of tape are transferred to the IC chips, chippackages or PCBs in the assembly line using simple, inexpensiveequipment that requires less precision.

The advantages of the present invention include the following: Becausethe solder forms are pre-positioned on the roll of tape off-line, theprocess of transferring the balls to the chips, chip packages or PCBs inthe assembly line can be performed much faster. The step of positioningand placing the solder forms on the roll of tape off-line saves time byperforming it concurrently or independently of processing of thesemiconductor chips. In addition, the present invention provides theflexibility of changing the design of the tape or the placement of thesolder forms off-line and inspecting the solder forms off-line, thus nottying up the assembly line. Also, since all the modifications are madeoff-line, the changes can be made in a shorter amount of time. Modifyingan assembly line is significantly harder than modifying off-lineequipment or products since an assembly line may be used for variousother products, and modifying the assembly line for one particularproduct line may affect other product lines. Furthermore, in the presentinvention, because the solder forms are pre-positioned and placed on aroll of tape, any rework or replacement of the solder forms becomessimple since the work can be performed on a low precision reworkstation.

SUMMARY OF THE INVENTION

The present invention provides cost-effective and time-saving methodsfor transferring solder forms to electronic components such as IC chips,ball grid array chip packages or PCBs by (a) positioning and placing thesolder forms on a roll of tape off-line and (b) transferring the solderforms to the electronic components in an assembly line.

More specifically, a method of transferring solder forms to electroniccomponents having conductive pads includes the following steps: (a)positioning and temporarily placing a plurality of sets of the solderforms on a roll of tape, (b) aligning a first set of the solder forms tothe conductive pads of a first one of the electronic components, (c)releasing the first set of the solder forms from the roll of tape, and(d) contacting the first set of the solder forms to the conductive padsof the first one of the electronic components. The steps (c) and (d) maybe interchanged depending on how the solder forms are placed on the rollof tape.

In the preferred embodiment of the present invention, a method oftransferring portions of a tape with solder forms to electroniccomponents having conductive pads includes the following steps: (a)positioning and permanently attaching a plurality, of sets of the solderforms in through-holes of the tape, (b) cutting a first portion of thetape having a first set of the solder forms, (c) aligning the first setof the solder forms to the conductive pads of a first one of theelectronic components, and (d) attaching the first set of the solderforms to the conductive pads of the first one of the electroniccomponents.

In the preferred embodiment, when a tape portion is attached to anelectronic component, the tape is a thermally conductive andheat-resistant elastomer that may have impregnated materials such asceramic to improve its thermal property. Such ceramic may be aluminumnitride. The tape may also contain solder flux to improve solderability.Thus the tape may include ceramic and/or solder flux.

The solder forms may be temporarily or permanently attached to the rollof tape. In the first instance, only the solder forms are transferred.In the latter case, portions of the tape are transferred to theelectronic components with the solder forms. The solder forms may beattached to one side of the tape or in through-holes in the tape usingeither UV sensitive adhesives or cold adhesives such as solder flux. Thesolder forms may be released by pressing the solder forms against theelectronic components, exposing the UV sensitive adhesives to a UV lightsource or using a "bed of nails". In addition, the solder forms may beshaped as balls, cylinders, polygonal boxes, barrels or hour glasses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a section view of a prior art ball grid array chip package.

FIG. 1B is a bottom plan view of fully-populated solder forms on thechip package shown in FIG. 1.

FIG. 1C is a bottom plan view of partially-populated solder forms on thechip package shown in FIG. 1.

FIG. 2 presents a prior art method of transferring solder forms to achip package using a fixture.

FIG. 3A presents a step of positioning and placing solder forms on aroll of tape off-line according to a first embodiment of the presentinvention.

FIG. 3B presents a step of feeding the roll of tape and aligning a chippackage to an array of solder forms in an assembly line according to thefirst embodiment of the present invention.

FIG. 3C presents a step of bringing the chip package and the solderforms in contact according to the first embodiment of the presentinvention.

FIG. 3D presents a step of releasing the solder forms from the tapeaccording to the first embodiment of the present invention.

FIG. 3E presents a step of feeding the roll of tape and aligning a newchip package to an array of solder forms according to the firstembodiment of the present invention.

FIG. 4A is an elevation view of solder forms attached to one side of aroll of tape.

FIG. 4B is an elevation view of solder forms attached to the pluralityof holes in a roll of tape.

FIG. 4C is an elevation view of a "bed of nails" used to release solderforms from a tape.

FIG. 4D is a perspective view of different shapes of solder forms thatmay be used in the present invention.

FIG. 5A presents a step of positioning and placing solder forms on aroll of tape off-line according to the preferred embodiment of thepresent invention.

FIG. 5B presents a step of feeding the roll of tape and cutting aportion of the tape having an array of solder forms in the assembly lineaccording to the preferred embodiment of the present invention.

FIG. 5C presents a step of aligning a chip package to the tape portionaccording to the preferred embodiment of the present invention.

FIG. 5D presents a step of attaching the tape portion to the chippackage according to the preferred embodiment of the present invention.

FIG. 5E presents a step of feeding the roll of tape and cutting anotherportion of the tape having an array of solder forms according to thepreferred embodiment of the present invention.

FIG. 6 is a perspective view of the roll of tape in FIG. 5B after thetape portion is cut out.

FIG. 7 is a top plan view of one embodiment of the present invention fortransferring a portion of a tape with solder forms to a chip package.

FIG. 8 is a top plan view of one embodiment of the present invention fortransferring only the solder forms to a chip package.

FIG. 9 presents a section view of a chip package that is integral withsolder forms, a tape portion and a PCB.

FIG. 10 is a section view of various hole shapes in a roll of tape.

DETAILED DESCRIPTION OF THE INVENTION

A tape carrier with solder forms and methods of transferring solderforms to integrated circuit (IC) chips, chip packages or printed circuitboards (PCBs) are disclosed. One embodiment of the present inventionincludes holding the solder forms on a roll of tape temporarily andtransferring only the solder forms to the chip package. The preferredembodiment of the present invention includes holding the solder forms ona roll of tape permanently and transferring both the solder forms and aportion of the tape to the chip package. Although the descriptions thatfollow describe various solder forms transfer processes mainly withreference to chip packages that are of a ball grid array type, solderforms may be transferred not only to chip packages but also to IC chipsor PCBs.

Transferring Solder Forms

FIGS. 3A-3E illustrate the steps of holding solder forms 31 on a roll oftape 33 temporarily and transferring only solder forms 31 from tape 33to a chip package 30 according to the first embodiment of the presentinvention. At step 3-1, solder forms 31 are temporarily attached to rollof tape 33 in a pattern that matches the pattern of pads 32 on chippackage 30. Step 3-1 is performed off-line (a non-device packageassembly line area). This step can be performed as the chips are beingmanufactured or before the chips are manufactured instead of waitinguntil the end of the chip manufacturing process, thus saving time. Inthe prior art, all of the steps including alignment of the solder formsare performed in the assembly line after the chips are manufactured.

In the present invention, if solder forms 31 are to be transferred tochip packages or PCBs, solder forms 31 may be aligned to tape 33mechanically, electro-mechanically or optically. There are manydifferent embodiments for performing step 3-1. In one embodiment, tape33 may have sprocket holes to engage with sprockets. After indexing tape33 into position, solder forms 31 can be mechanically placed on tape 33using a pre-programmed mechanical arm. For an optical alignment, tape 33may have punched holes or targets. Also, one may use fixtures, pins andrelays to establish alignment. Although step 3-1 requires a highprecision alignment, because it can be performed concurrently with thechip processing or independent of the chip processing, it ultimatelysaves time in transferring solder forms 31 to chip package 30 sincesteps 3-2 through 3-4 are basic and fast.

If solder forms 31 are to be transferred to chips, a photolithographicprocess may be employed in step 3-1 to position and place solder formson tape 33 since the solder forms pattern for chips requires tightertolerance. Various photolithographic processes including, but notlimited to, optical, electron beam, X-ray and deep-UV lithographies canbe utilized. The solder forms can be deposited on tape 33 using aplating process or a vapor deposition process.

One embodiment using an optical photolithographic process and a platingprocess is described below. Tape 33 is coated with a thin metal layerand a dry photoresist layer. After exposing light to the areas wheresolder forms 31 are to be placed, the resist films from the exposedareas are developed out. Tape 33 is placed in a plating bath to platesolder material in the areas where the resist films have been removed.After plating, the photoresist layer is stripped, and the thin metallayer is etched, leaving solder forms 31 on tape 33 as shown in FIG. 3A.

Being able to fabricate a roll of tape having solder forms off-line isadvantageous because not only it is cost-effective but also the solderforms and their alignments can be inspected off-line, thus saving time.

Steps 3-2 through 3-5 are performed typically in a device packageassembly line using inexpensive, low precision equipment. At step 3-2,as tape 33 is fed from one side, it is rewound on the other side. Chippackage 30 and the solder forms pattern on tape 33 are aligned using amechanical, electromechanical or optical alignment scheme, as describedlater with reference to FIG. 8. Although the placement of solder forms31 on tape 33 in step 3-1 requires high precision to place each solderform accurately on tape 33, step 3-2 can be accomplished with lowaccuracy in batch operation since an array of solder forms 31 aretransferred at once.

At step 3-3, chip package 30 is brought in contact with solder forms 31on tape 33. At step 3-4, solder forms are released from tape 33 andattached to chip package 30. At step 3-5, tape 33 is indexed, and a newchip package 35 is positioned so that steps 3-2 through 3-4 can berepeated. It will be appreciated that multiple rolls of tape may beprocessed simultaneously at steps 3-1 through 3-5. Also, multiple chippackages may be handled simultaneously for each roll of tape at steps3-2 through 3-5 to speed up the process.

Tape Structures, Solder Forms Shapes and Release Mechanisms

FIGS. 4A-4D illustrate various tape structures, solder forms shapes andsolder forms release mechanisms. In FIG. 4A, solder forms 41 aretemporarily attached to one side of a roll of tape 43. Various adhesivesincluding, but not limited to, sticky solder flux and UV sensitiveadhesives that release solder forms 41 upon exposure to UV light can beused between solder forms 41 and tape 43.

FIG. 43 presents solder forms 44 placed in plurality of holes in a rollof tape 45. Solder forms 44 are attached to tape 45 in similar mannersas solder forms 41 in FIG. 4B. Tape 45 has good thermal conductivity andheat resistance characteristics. In one embodiment, tape 45 may be madeof an organic material such as an elastomer and have impregnatedmaterials including, but not limited to, ceramic and solder flux. Suchceramic may be aluminum nitride. It should be noted that solder flux canbe impregnated in a tape or put on the entire tape, on solder forms, oron areas between solder forms using a printing or screen printingprocess. While tape 43 or 45 may be used for the process described inFIGS. 3A-3E, tape 45 is used for the process described in FIGS. 5A-5E.When a tape is used for the process described in FIGS. 3A-3E, the tapemay be reused since only the solder forms are transferred to chippackages.

The present invention may utilize a variety of solder forms releasemechanisms. In one embodiment, when UV adhesives are used between solderforms 44 and tape 45 or between solder forms 41 and tape 43, exposure ofthe adhesives to UW light releases the solder forms from the tape. Inanother embodiment, a "bed of nails" 49 may be used as shown in FIG. 4Cto release solder forms 47 from a tape 48. Bed of nails 49 may includemultiple rods or poles 46 arranged in a pattern that matches the patternof a set of solder forms 47 so that bed of nails 49 can push solderforms 47 out of holes 42 in tape 48. When bed of nails 49 is used, theorder of the steps 3-3 and 3-4 in FIGS. 3C and 3D are reversed; that is,solder forms 31 are first released from tape 33 using bed of nails 49and then attached to chip package 30. Yet, in another embodiment, a chippackage may be merely pressed against the solder forms to attach thesolder forms to the chip package. In the last embodiment, the adhesionstrength between the solder forms and the tape 43 must be lower than theadhesion strength between the solder forms and the pads on the chippackage to transfer the solder forms to the chip package.

The present invention may also incorporate a variety of different shapesof solder forms including, but not limited to, those shown in FIG. 4D. Asolder forms may be of a ball shape 50, a cylinder shape 51, a barrelshape 52, a hourglass shape 53 or a polygonal box shape 54.

Transferring Solder Forms and Tape Portion

The preferred embodiment of the present invention is shown in FIGS.5A-5F illustrating how both solder forms 61 and a portion 64 of a rollof tape 63 can be transferred from tape 63 to a chip package 65. At step5-1, solder forms 61 are aligned and placed on a roll of tape 63 using asimilar procedure as the one described with respect to step 3-1 in FIG.3A. Like step 3-1, step 5-1 is performed off-line (a non-device packageassembly line). Steps 5-2 through 5-5 are performed in a device packageassembly line using inexpensive, low precision equipment. At step 5-2,tape 63 is fed from one end and rewound at the other end. A tape portion64 is cut so that both solder forms 61 and tape portion 64 can beremoved from tape 63. In the preferred embodiment, because portions oftape 63 are cut away, unlike tape 33, tape 63 cannot be reused. FIG. 6shows a top plan view of tape 63 after portion 64 has be removed.

At step 5-3, chip package 65 and the solder forms pattern on tapeportion 64 are aligned to each other using a mechanical,electromechanical of optical alignment scheme, as described later withreference to FIG. 7. At step 5-4, chip package 65 comes in contact withsolder forms 61 and tape portion 64. At step 5-5, tape 63 is indexed tocut another tape portion 66 for the next chip package, and the steps 5-3through 5-5 are repeated. Like steps 3-1 through 3-5 in FIGS. 3A-3E, itwill be appreciated that multiple rolls of tape may be processedsimultaneously at steps 5-1 through 5-5. Also, multiple chip packagesmay be handled simultaneously for each roll of tape at steps 5-2 through5-5 to speed up the process.

One Detailed Embodiment for Transferring Solder Forms and Tape Portion

There are many different implementations for transferring portions of atape with solder forms to electronic components such as chips, chippackages or PCBs. FIG. 7 illustrates one embodiment for mechanicallytransferring tape portions with solder forms to electronic components,corresponding substantially to steps 5-2 through 5-4 in FIGS. 5B-5D. Aroll of tape 70 having arrays of solder forms 78 is fed by a sprocketdrive (not shown). When an array of solder forms is at a location 74, apuncher (not shown) punches out a portion 75 of tape 70, and portion 75having solder forms is dropped to a rotatable tray 72. A mechanical arm(not shown) places electronic components 77 such as chip packages, chipsor PCBs on the bottom side of a rotatable table 73. When an electroniccomponent and a tape portion having solder forms are rotated to aposition 76, the electronic component is pressed against the tapeportion to attach the tape portion with the solder forms to theelectronic component. After the attachment, the electronic componentwith the tape portion and the solder forms may be left on rotatabletable 73 or on rotatable tray 72 to be picked up by another mechanicalarm.

One Detailed Embodiment for Transferring Solder Forms Only

There are also numerous embodiments for transferring only the solderforms from a roll of tape to electronic components. For illustration,FIG. 8 shows one embodiment for mechanically transferring solder formsto electronic components, corresponding substantially to steps 3-2through 3-4 in FIGS. 3B-3D. A roll of tape 80 having arrays of solderforms is fed by a sprocket drive (not shown). Electronic components 84are placed on the bottom of a rotatable table 83. When an electroniccomponent and an array of solder forms are positioned at a location 85,solder forms are transferred from tape 80 to the electronic component bypushing down rotatable table 83 against tape 80, pushing up tape 80against rotatable table 83, or moving both rotatable table 83 and tape80 down and up, respectively. The electronic component having the solderforms are removed from rotatable table 83 using another mechanical arm.

Chip Package with Solder Forms and Tape Portion Coupled to PCB

Now referring to FIG. 9, after a chip package 90 receives solder forms94 with a tape portion 93, chip package 90 can be attached to a PCB 92making electrical connections through solder forms 94. It should benoted that a chip package may be attached to a PCB without the tapeportion. Having tape portion 93 between chip package 90 and PCB 92provides the following advantages: Tape portion 93 may carry flux, asdescribed before, keeps debris away from solder forms 94, preventssolder forms 94 from moving into non-designated areas, provides highthermal conductivity, may have impregnated materials to improve furtherthe thermal conductivity, thermal stability, mechanical stability and/orelectrical characteristics, distributes stress over tape portion 93, andprovides a fixed spacing between the bottom of chip package 90 and thetop of PCB 92. In addition, tape portion 93 can provide various solderforms shapes including, but not limited to, 100, 101, 102 and 103, asshown in FIGS. 10A-10D. Depending on the specific implementation, oneshape may produce less stress in the solder forms than others.

While the present invention has been particularly described withreference to the various figures, it should be understood that thefigures are for illustration only and should not be taken as limitingthe scope of the invention. Many changes and modifications may be madeto the invention, by one having ordinary skill in the art, withoutdeparting from the spirit and scope of the invention as disclosedherein.

What is claimed is:
 1. An integrated circuit package assembly,comprising:an integrated circuit package that has a surface pads; atape; a solder pre-form located on said tape; and, an adhesive that islocated between said tape and said solder pre-form, and attaches saidsolder pre-form to said tape and allows said solder pre-form to beattached to said surface pad of said integrated circuit package.
 2. Theassembly as recited in claim 1, wherein said tape has a hole thatreceives said solder pre-form.
 3. The assembly as recited in claim 1,wherein said solder pre-form has a spherical shape.
 4. The assembly asrecited in claim 1, wherein said solder pre-form has a rectangularshape.